Tom, 

I’m slightly confused by your question.

First, Sonos doesn’t ’play’ on your phone. The controller is merely an interface to see what is being played by the speaker, there is no music going through it. 

Second, there are two different ‘inputs’ being ‘used’ by the two devices. The Apple TV, presumably, is connected to your TV with an HDMI cable, and presumably playing to a Sonos soundbar of some type via HDMI ARC. So, you’re likely not using the Sonos app to ‘get’ the data, but instead some other App on the Apple TV to ‘play’ the music. 

The Sonos speakers, when you use the Sonos controller, go out and grab the music from an Apple (or other streaming service) server. Many people assume it’s a Sonos server, but it isn’t. So it’s possible that Apple has a different server set up to feed appropriate data to Sonos devices that are reaching out to get and play music.

The iOS app shows what is playing on my Arc, currently as Multichannel PCM 5.1. You can see this on the screencap below. If you need, I can pull out my iPhone, and show you the same thing with a screencap from there. I happen to be typing this on my iPad  

Am I misunderstanding your question?

The app doesn’t display the music format. The now playing screen will show if lossless is playing via Apple Music. But it won’t show specific data like format/bit rate/depth for other streaming sources afaik. If I’m wrong would love to know as well. 
 

For other sound sources you can check Settings>General Settings > About Your System look for the player name. 

Thanks for the explanation Bruce.

If you want to see the sample rate and bit size when streaming music, try my apps (see profile). Codec is not shown as it is not exposed by the system.

Moderator Note: Adjusted uploaded screenshot. Modified in accordance with the Community Code of Conduct.